1. Field of the Invention
The present invention relates to a light emitting head that irradiates light, an information storage device that uses the light emitting head to access information on a predetermined recording medium, and a manufacturing method for manufacturing a composite head having the light emitting head.
2. Description of the Related Art
As the information society evolves, the amount of information continues to grow. In response to the increase in the amount of information, there has been a demand for the development of an information recording scheme or an information storage device with a dramatically high recording density.
In optical disk devices that record and reproduce information to and from a recording medium (optical disk) by means of a spot of light, reducing the size of the spot impinging on the recording medium has provided a high density. The spot size concentrated by lenses, however, has recently been approaching a limit because it can theoretically be reduced to as much as the wavelength of the incident light. Therefore, as a recording scheme that enables the spot size to be further reduced to provide further high density recording, attention has been attracted onto a near field optical recording scheme that uses a near field light emanated from a micro aperture smaller than a wavelength of an incident light to form a smaller spot size than the wavelength. This near field optical recording scheme employs, as a light emitting head, a near field optical head that includes such a micro aperture and propagates light to the micro aperture to generate the near field light.
For a micro aperture in a near field optical head, for example, there is known an aperture provided on a tip of a sharpened optical fiber, as described in Japanese Patent Publication No. 10-206660. The aperture is fabricated by coating an optical fiber, which has a tip sharpened by heating and drawing the fiber or using a selective chemical etching with buffered hydrofluoric acid, with a metal film, and removing a part of the coated and sharpened tip using particle beam, such as focused ion beam (FIB) and the like. There are also known techniques that improve propagation efficiency of light or spot size by modifying tip shape of a optical fiber (for example, see Opt. Rev. vol. 5, No. 6 (1998) 369–373 and Appl. Phis. lett., vol. 73, No. 15).
Another technique for fabricating a micro aperture in a near field optical head is disclosed in U.S. Pat. No. 5,689,480, in which a funnel-shaped aperture is created in a planar plate. In this technique, a Si substrate is patterned using lithographic techniques to provide a rectangular pattern on the substrate, then the pattern is subjected to anisotropic etching taking advantage of a crystal orientation of the substrate to create a recess of inverted pyramid shape, and the apex of the inverted pyramid, which represents the deepest point in the substrate, is passed through the back side of the substrate by polishing or etching on the back side of the Si substrate.
Japanese Patent Publication No. 2004-30840 discloses a light emitting head (near field optical head) having a simple shape of two-dimensional geometry which can be produced by lithographic techniques such as using a stepper exposure apparatus. In a technique disclosed in Japanese Patent Publication No. 2004-30840, a transparent dielectric is layered on a substrate, the dielectric is covered with a metal after patterned, and a small aperture is created by cutting an exit portion using FIB and the like to generate near field light.
In conventional near field light recording schemes, however, there is a problem of utilization efficiency of light being several orders of magnitude lower than in a lens optical system. A further problem arises in that metal films are produced to form a micro aperture, and non-negligible leakage light is produced at the border between the aperture and films in addition to a main spot generated in the aperture.
In conventional method of creating a micro aperture, there is also a problem of the variation in the diameter of the created aperture due to errors in a drilled location of a micro aperture, the film thickness of a metal film, and the length of the medium itself which propagates light. Consequently desired propagation efficiency or electromagnetic fields cannot be obtained. In addition, in case of multiple heads for example, there arises a problem regarding a relative location to other heads when processes are repeated on each near field optical head to make the diameter to a desired size; in this case, the distance from a head to a recording medium varies on a head basis due to variation in drilled locations, even when each head has the same diameter. The conventional near field optical head thus suffers from the problems in the fabricating processes.
Moreover, it is conceivable that the near field optical head is not used alone but requires a magnetic head such as those in a magneto-optical (MO) disk device and light assisted magnetic recording/reproducing device. The light assisted magnetic recording/reproducing device is particularly hopeful to provide a recording capacity over 1 Tb. In the light assisted magnetic recording/reproducing device, light emitted from a light emitting head is irradiated onto a magnetic recording medium in writing information so that the temperature of the magnetic recording medium rises and, immediately after that, a magnetic field generated by a recording magnetic head writes the information. A reproducing magnetic head is used to read the information in reading the information. Advantages of the light assisted magnetic recording/reproducing device include the facts that information can be written with low magnetic field intensity in the magnetic recording medium, and a problem of thermal fluctuation can be avoided because records are fixed once the temperature decreases. These devices, however, are required to generate magnetism near the light-irradiating area. It is practically impossible to mount a magnetic head on a near field optical head, which uses fibers and lenses, with an accuracy corresponding to a track pitch of the recording media. Although in the near field optical head disclosed in Japanese Patent Publication No. 2004-30840, a magnetic head can be integrated into it using lithographic techniques, the near field optical head has an aperture diameter of several hundreds nanometers and a light spot is formed in the center of the aperture, causing the light spot to be located away from the magnetic head by a distance at least half of the aperture diameter. Given the fact that the track pitch is about 20 nm for 1 Tb recording density, if a light spot is located away from a magnetic head by 100 nm or more, a problem arises in that light and magnetism are irradiated and generated in a different track when both heads are moved by an arm and the like to incline with respect to the track. Therefore, the conventional near field optical head also has a problem regarding its alignment.